1. Field of the Invention
The present invention relates to signal reception in a communication system. More particularly, the present invention relates to a signal receiving apparatus and method adapted for use with a time-variant channel.
2. Description of the Related Art
In general, in a communication system including a transmitting side and a receiving side, the receiving side must know a current decision value of a signal received by the receiving side in order to estimate a characteristic of a channel. Herein, the decision value means transmission information restored. At this time, after an elapse of a certain training period of time, the use of the decision value obtains a channel estimate obtained by assuming the characteristic of a channel over which a transmitting signal has been transmitted.
In a case where a conventional signal receiving apparatus estimates the characteristic of a channel varying with time, a reduction in a time delay of the estimated channel characteristic requires a decrease in time spent in estimating the decision value. For this purpose, for example, in Maximum-Likelihood Sequence Estimation (hereinafter, referred to as “MLSE”), a tentative decision value determined with reducing a depth of a traceback is used. Herein, MLSE may also be called Maximum Likelihood Sequence Detection (MLSD), which is described in Proakis, “Digital Communications,” Prentice Hall Press, pp. 583–602 (1995). However, since the tentative decision value has a high error rate, there has been a problem in that the characteristic of a channel estimated using the tentative decision value also has an increased error. Consequently, the above-mentioned conventional signal receiving apparatus has a disadvantage in that since there is a significant difference between the estimated characteristic of a channel and the real characteristic of a channel, a decision value used to restore user information cannot be estimated correctly from the estimated channel characteristic with an error.
To overcome this problem, another conventional signal receiving apparatus employs a linear predictor for estimating the characteristic of a time-delayed channel and predicting the characteristic of a current channel from the estimated characteristic of a delayed channel. Herein, the linear predictor can be embodied through a Wiener solution utilizing an autocorrelation of a channel, as is known to those skilled in the art. For the sake of simplicity of the solution, a method of linearly predicting the characteristic of a channel in which only a gradient of the channel is estimated and the channel is approximated with a linear function may be used. However, in the above-mentioned conventional signal receiving apparatus, there also arises a problem in that when the range of the characteristic of a channel to be predicted is long, the above-mentioned predictors cannot correctly predict the characteristic of a channel. Thus, the latter of two conventional signal receiving apparatuses, similar to the former mentioned above, also employs a tentative decision value, so that an error of the tentative decision value contributes to an incorrect restoration of user information.